Stationary gas turbines have been in use for several years, in particular in association with steam turbines for producing electricity, and in particular in co-generation applications, i.e. applications where both mechanical work and heat energy are supplied simultaneously.
At present, although the overall mechanical efficiency of the most recent gas turbines is as good as that of steam turbines, the efficiency of gas turbines is nevertheless degraded for an expansion turbine by the need to produce work to compress air. This work becomes all the greater because in order to avoid excessively hot gases damaging the turbine, it has appeared necessary to compress an excess amount of air together with the oxidizing air, with the excess often being greater than twice the volume of the oxidizing air. At present, the maximum limiting temperature that can be accepted by expansion turbines exceeds 1000.degree. C., but cannot be raised significantly beyond about 1250.degree. C.
It will also be observed that the overall mechanical efficiency of a gas turbine is naturally highly sensitive to the polytropic efficiency of the turbo compressor.
Furthermore, at equal power, the size of the expansion turbine of "gas turbines" that must produce work firstly for driving the compressor is considerably greater than the size of a steam turbine and it increases very quickly with decreasing mechanical efficiency.
Finally, it is necessary to provide an air compressor driven by the shaft of the gas turbine, and the size of the compressor also increases very quickly with decreasing mechanical efficiency of the compressor.
It should also be remembered that for purposes of protecting the environment, efforts are now being made with combustion heat engines to reduce emissions of nitrogen oxides.
One technique that is well known consists in acting at source by "quenching" the flame with liquid water or steam as close as possible to the reaction zones.
However, since water is injected to give rise to a quenching phenomenon, the injection must be under accurate control and must be quantitatively limited to avoid any deterioration of combustion proper, and in particular to avoid any carbon monoxide appearing.
In addition, "quenching" the flame is of limited efficiency since it acts only on the time spent at high temperature by elements that may combine to form nitrogen oxides (NOx) without acting on the maximum temperature reached within the reaction zone or on the adiabatic combustion temperature.
The present invention seeks to remedy the above-mentioned drawbacks and to enable a natural gas turbine system to be implemented which makes it possible both to reduce the size of the rotary machines used, and to improve performance from the energy, mechanical, and, in the event of co-generation, thermal points of view, while simultaneously providing better protection for the environment.